To assess the presence of neutralizing antibodies for hepatitis C virus (HCV) in an experimental intravenous immune globulin (IGIV) preparation enriched in antibodies to HCV, the residual infectivity of an HCV inoculum was measured using two chimpanzees (see Z01 BQ04015-01). The experimental chimpanzee received 1 mL of a diluted H-strain HCV inoculum containing 64 CID50 pre-incubated in vitro with an IGIV prepared solely from anti- HCV EIA-2 reactive plasma units and had relatively high levels of antibodies to HCV envelope proteins (E1 and E2) while the control chimpanzee received the same inoculum preincubated with a commercial IGIV prepared from EIA -2 screened plasma and devoid of both anti-E1 and anti-E2. Both IGIVs were solvent/detergent (S/D) treated. 17 months post infusion, neither chimpanzee showed signs of HCV infection, i.e., elevation of alanine aminotransferase (ALT) and presence of HCV RNA in their weekly serum specimens. Anti- HCV was only detected in sera of the experimental chimpanzee due to passive immunization; at weeks one through seven post infusion, with peak titers of 1:8 at weeks one through four. The lack of infectivity in the control chimpanzee might be due to the low titer of the inoculum used. We need to repeat the same experiment using an H inoculum standardized for low infectivity (provided by Dr. R. Purcell of NIH). Previously (see Z01 04017-01 LPLD ) we set up EIAs to measure anti- E1and anti- E2 using partially purified glycoproteins derived from baculovirus constructs, HCV - Bac 3 and HCV - Bac 5, respectively. However, HCV - Bac 5 not only can express E2 fusion protein but also a full-length E1. The E1 did not react with any plasma or IGIV tested in Western blots and hence was assumed not to be reactive in EIA which utilizes the native form of proteins from HCV-Bac 5. An experimental anti-E2 EIA kit (kindly provided by Abbott Laboratories) was subsequently employed. The results were similar to those obtained with our EIA using proteins from HCV - Bac 5. Thus, data support that anti- HCV screening reduced levels of both anti- E1 and anti- E2 in plasma and the resulting immune globulins. Our previous thermal stability studies of albumin demonstrated no difference in the stabilization of a 5% albumin solution between the current albumin products using both caprylate (CA) and acetyltryptophanate (AT) at 0.08 mmole/g albumin each and the use of CA alone. A manufacturer recently submitted the conformance lots and has since been approved for producing three formulations (5, 20, 25%) of Albumin (Human) containing only CA as a single stabilizer. Several such lots along with the corresponding parent lots containing both CA and AT were evaluated by HPLC for monitoring molecular integrity. All were within the specification which we established for albumin and immune globulin products, i.e., monomer + dimer greater than 90%. We have also performed similar HPLC analyses for an IGIV product by one manufacturer and various intramuscular immunoglobulin products by two manufacturers because of their introduction of a S/D incubation step for improved viral safety of their products. All revised products had little or no aggregates and fragments and met the specifications. Stability studies of these new products are ongoing to ensure that the performed similar HPLC analyses for an IGIV product by one manufacturer and various intramuscular immunoglobulin products by two manufacturers because of their introduction of a S/D incubation step for improved viral safety of their products. All revised products had little or no aggregates and fragments and met the specifications. Stability studies of these new products are ongoing to ensure that the molecular integrity will be maintained throughout the dating period.